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本文主要研究一下rocketmq的NettyEncoder及NettyDecoder
NettyEncoder
org/apache/rocketmq/remoting/netty/NettyEncoder.java
public class NettyEncoder extends MessageToByteEncoder<RemotingCommand> {
private static final Logger log = LoggerFactory.getLogger(RemotingHelper.ROCKETMQ_REMOTING);
@Override
public void encode(ChannelHandlerContext ctx, RemotingCommand remotingCommand, ByteBuf out)
throws Exception {
try {
ByteBuffer header = remotingCommand.encodeHeader();
out.writeBytes(header);
byte[] body = remotingCommand.getBody();
if (body != null) {
out.writeBytes(body);
}
} catch (Exception e) {
log.error("encode exception, " + RemotingHelper.parseChannelRemoteAddr(ctx.channel()), e);
if (remotingCommand != null) {
log.error(remotingCommand.toString());
}
RemotingUtil.closeChannel(ctx.channel());
}
}
}
- 这里继承MessageToByteEncoder,类型是RemotingCommand,先写入header再写入body
RemotingCommand.encodeHeader
org/apache/rocketmq/remoting/protocol/RemotingCommand.java
public ByteBuffer encodeHeader() {
return encodeHeader(this.body != null ? this.body.length : 0);
}
public ByteBuffer encodeHeader(final int bodyLength) {
// 1> header length size
int length = 4;
// 2> header data length
byte[] headerData;
headerData = this.headerEncode();
length += headerData.length;
// 3> body data length
length += bodyLength;
ByteBuffer result = ByteBuffer.allocate(4 + length - bodyLength);
// length
result.putInt(length);
// header length
result.put(markProtocolType(headerData.length, serializeTypeCurrentRPC));
// header data
result.put(headerData);
result.flip();
return result;
}
- 这里先写数据总长度,再写入header长度,最后写入header的数据,在写入body数据
- 整体结构为:Length | Header length | Header data | Body
NettyDecoder
org/apache/rocketmq/remoting/netty/NettyDecoder.java
public class NettyDecoder extends LengthFieldBasedFrameDecoder {
private static final Logger log = LoggerFactory.getLogger(RemotingHelper.ROCKETMQ_REMOTING);
private static final int FRAME_MAX_LENGTH =
Integer.parseInt(System.getProperty("com.rocketmq.remoting.frameMaxLength", "16777216"));
public NettyDecoder() {
super(FRAME_MAX_LENGTH, 0, 4, 0, 4);
}
@Override
public Object decode(ChannelHandlerContext ctx, ByteBuf in) throws Exception {
ByteBuf frame = null;
try {
frame = (ByteBuf) super.decode(ctx, in);
if (null == frame) {
return null;
}
ByteBuffer byteBuffer = frame.nioBuffer();
return RemotingCommand.decode(byteBuffer);
} catch (Exception e) {
log.error("decode exception, " + RemotingHelper.parseChannelRemoteAddr(ctx.channel()), e);
RemotingUtil.closeChannel(ctx.channel());
} finally {
if (null != frame) {
frame.release();
}
}
return null;
}
}
- 这里继承LengthFieldBasedFrameDecoder,maxFrameLength为FRAME_MAX_LENGTH,lengthFieldOffset为0,lengthFieldLength为4,lengthAdjustment为0,initialBytesToStrip为4
- 获取ByteBuffer之后调用RemotingCommand.decode(byteBuffer)
RemotingCommand.decode
org/apache/rocketmq/remoting/protocol/RemotingCommand.java
public static RemotingCommand decode(final ByteBuffer byteBuffer) {
int length = byteBuffer.limit();
int oriHeaderLen = byteBuffer.getInt();
int headerLength = getHeaderLength(oriHeaderLen);
byte[] headerData = new byte[headerLength];
byteBuffer.get(headerData);
RemotingCommand cmd = headerDecode(headerData, getProtocolType(oriHeaderLen));
int bodyLength = length - 4 - headerLength;
byte[] bodyData = null;
if (bodyLength > 0) {
bodyData = new byte[bodyLength];
byteBuffer.get(bodyData);
}
cmd.body = bodyData;
return cmd;
}
public static int getHeaderLength(int length) {
return length & 0xFFFFFF;
}
private static RemotingCommand headerDecode(byte[] headerData, SerializeType type) {
switch (type) {
case JSON:
RemotingCommand resultJson = RemotingSerializable.decode(headerData, RemotingCommand.class);
resultJson.setSerializeTypeCurrentRPC(type);
return resultJson;
case ROCKETMQ:
RemotingCommand resultRMQ = RocketMQSerializable.rocketMQProtocolDecode(headerData);
resultRMQ.setSerializeTypeCurrentRPC(type);
return resultRMQ;
default:
break;
}
return null;
}
- 这里先获取header长度,获取header的数据,decode出来RemotingCommand,之后获取body
小结
rocketmq的netty编码解码,使用的是RemotingCommand对象,编码继承MessageToByteEncoder,解码采用的是LengthFieldBasedFrameDecoder
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